My Neverwinter character has advanced steadily through level 31, halfway to the game's level cap. If you're looking for a decent single player experience with little (though probably not zero) money down, the game seems to fit the bill. If you play MMO's because you are seeking to fill every gear slot on your character with a reasonable quality item, you're in for an expensive and frustrating haul. The question I can't quite answer yet is to what extent your stats matter.

The Gameplay

According to the game's map, I've seen fewer than half of the zones, though some of these areas may be dungeons and/or level 60 endgame areas. The game plays roughly like other recent MMO's, with click-to-attack, a requirement to play in mouse-look mode (which is clunky when it comes to actually using anything on the UI), and lots of dodge-rolling in response to red danger zones on the ground.

One innovation on this point is that you are not actually required to get OUT of the red area - as long as you perform a dodge roll, the game will treat you as having dodged that attack, so you can get back to killing and don't need to worry about failing to travel far enough for whatever reason. (I guess this is technically consistent with Dungeons and Dragons rules, where making a saving throw against something does not necessarily physically move the character out of the way?) I don't generally play rogue type characters, but with all the rolling around that you have to do regardless and less penalty than normal for being caught in melee range, an agile character just feels right in this particular game.

Mechanics aside, it's a reasonably high production value game with about the requisite quests, some voice acting and cut-scenes, and basic MMO features. I haven't had trouble soloing on the rogue with a healing NPC companion - more on this in a minute - and thus far I haven't hit major roadblocks. Things could go downhill but overall it seems like the game is not out to stop me from getting to the level cap.

Filling the gearslotsI happened to have some Astral Diamonds I didn't have to pay for courtesy of some promotional codes, but if I had not I probably would not have spent money on the game to this point. I don't know where the cutoff is, but I expect that trying to get all the way to level cap without paying would be less pleasant. Even at this early level, pretty much everything can be upgraded to somehow boost your stats. The cost (generally in real money) of gear, item quality,etc, could be a major issue for someone approaching the game with an MMO min-max mindset. A few examples:

Almost all equipment has slots for enhancements. Refining enhancements (done by feeding them other unwanted enhancements and then using a consumable item that is not readily available without diamonds) is costly, and it's not clear that it's worthwhile; I'm finding rank 3-4 enhancements in loot now, so spending diamonds to upgrade my rank 1's would not have been a good plan.

Players can equip one artifact for stats and a special effect (like trinkets in other games), and two additional artifacts at max level for stats only. Costly upgrades are required to increase these in quality from green to blue and blue to purple. (There is also a purely cosmetic and even more costly upgrade to level 100 that does not appear to grant any additional stats, only change the tooltip to legendary orange status.)

Each character can have one active NPC companion and 2-4 additional companions (the slots unlock with levels 30 and 60) for passive stat bonuses. In addition to costs to obtain the companions, these guys also have quality tiers that affect both the companion's rank cap and their passive bonuses.

My top priority with my Diamonds was to obtain a healer NPC. Neverwinter characters don't have significant passive healing or food to heal up between combat, so either your character or your active companion just about has to be some kind of Cleric if you intend to solo. You receive a white quality Cleric for free at level 16, but this character is capped at rank 15 out of 30 due to its low quality; by most accounts, soloing at high levels will be unpleasant.

I don't know if you absolutely need to go all the way to Purple quality and rank 30 (though each companion has a third special ability that requires this rank), but paradoxically the cost of upgrading that companion was actually significantly higher (300K for white to green, 500K for green to blue, and 750K for blue to purple) than just buying a purple healer from a past promotion (about 600K) and not having to worry about the problem. This solution costs around $12 depending on the current exchange rate, and I'd consider it a near must have.

If I was paying out of pocket, I'm not sure what, if anything, I would buy. Since I didn't pay for my diamonds, I did spend a chunk on an upgraded mount, which moves twice as fast and can take significant more hits, in exchange for looking like a steampunk scorpion-mech. I spent my remaining diamonds on additional companions who offer passive bonuses I wanted to slot on my character for adventuring, while also providing a party of four companions to play the Sword Coast Adventures minigame on the web portal.

There are fees for storage, though I haven't had issues here. There are fees for respecing, but I either didn't screw up my build that badly or else haven't done anything hard enough for it to matter. The real place where the cost will be problematic would be if the game gets to the point where it's hard to scrape together enough DPS with non-upgraded gear. Of course, I don't care about PVP or even dungeons, so it's easier for me to shrug this side of the game off. If you play MMO's to acquire gear, this system - bearing in mind that acquiring the currency naturally is not especially convenient to create demand for currency resales, could be a deal-breaker.

A side effect to grabbing the cheapest purple quality healer and mount I could find is having a giant scorpion mech for a mount and a Lamia with a sword-harp for a companion. This tasteful stuff doesn't exactly fit the lore as far as I was aware, but at least it's not costing me anything out of pocket.